Fl. Peruv. 1: 43. 1798.
Plants annual or facultatively perennial. Vegetative stems submersed with elongate internodes, or emersed and procumbent. Flowering stems 1–9 cm, distal internode 0.5–4 cm. Sessile leaves forming basal rosette, blade linear to oblanceolate, thin, 2.4–3.7 cm × 3–8 mm. Petiolate leaves floating or emersed; stipule 1–5 cm; petiole 2–13 cm; blade reniform, 1–4 × 1–5 cm, length equal to or less than width, apex obtuse. Inflorescences spicate, 2–8-flowered, elongating in 1 day, usually shorter than spathes, terminal flower sometimes extending beyond spathe apex; spathes 0.8–5.5 cm, glabrous; peduncle 0.5–4.2 cm, glabrous. Flowers opening ca. 3 hours after sunrise, wilting by early afternoon; perianth white, salverform, tube 5–10 mm, limbs zygomorphic, lobes narrowly elliptic, 3–6.5 mm, distal central lobe with yellow or green region at base, sometimes with distal brown spot; stamens unequal, lateral stamens 0.9–2.2 mm, filaments linear, pubescent with white multicellular hairs toward apex; central stamen 2.2–4.7 mm, filament sparsely pubescent with multicellular hairs; style pubescent with multicellular hairs. Seeds 8–14-winged, 0.5–0.9 × 0.3–0.5 mm. 2n = 48.
Phenology: Flowering Jun–Oct.
Habitat: Roadside ditches, edges of streams and ponds, freshwater tidal mudflats
Elevation: 0–2600 m
Ala., Conn., Del., Fla., Ga., Ill., Ind., Ky., La., Md., Miss., Mo., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Tex., Va., W.Va., Mexico, throughout Central America, scattered in South America (Argentina, Brazil, Paraguay), naturalized in Italy.